The present invention relates to methods and apparatus for navigating, such as zooming and panning, over an image of an object in such a way as to provide the appearance of smooth, continuous navigational movement.
Most conventional graphical computer user interfaces (GUIs) are designed using visual components of fixed spatial scale, it has long been recognized, however, that visual components may be represented and manipulated such that they do not have a fixed spatial scale on the display; indeed, the visual components may be panned and/or zoomed in or out. The ability to zoom in and out on an image is desirable in connection with, for example, viewing maps, browsing through text layouts such as newspapers, viewing digital photographs, viewing blueprints or diagrams, and viewing other large data sets.
Many existing computer applications, such as Microsoft Word, Adobe Photo Shop, Adobe Acrobat, etc., include zoomable components. In general, the zooming capability provided by these computer applications is a peripheral aspect of a user's interaction with the software and the zooming feature is only employed occasionally. These computer applications permit a user to pan over an image smoothly and continuously (e.g., utilizing scroll bars or the cursor to translate the viewed image left, right, up or down). A significant problem with such computer applications, however, is that they do not permit a user to zoom smoothly and continuously. Indeed, they provide zooming in discrete steps, such as 10%, 25%, 50%, 75%, 100%, 150%, 200%, 500%, etc. The user selects the desired zoom using the cursor and, in response, the image changes abruptly to the selected zoom level.
The undesirable qualities of discontinuous zooming also exist in Internet-based computer applications. The computer application underlying the www.mapquest.com website illustrates this point. The MapQuest website permits a user to enter one or more addresses and receive an image of a roadmap in response. FIGS. 1–4 are examples of images that one may obtain from the MapQuest website in response to a query for a regional map of Long Island, N.Y., U.S.A. The MapQuest website permits the user to zoom in and zoom out to discrete levels, such as 10 levels. FIG. 1 is a rendition at zoom level 5, which is approximately 100 meters/pixel. FIG. 2 is an image at a zoom level 6, which is about 35 meters/pixel. FIG. 3 is an image at a zoom level 7, which is about 20 meters/pixel. FIG. 4 is an image at a zoom level 9, which is about 10 meters/pixel.
As can be seen by comparing FIGS. 1–4, the abrupt transitions between zoom levels result in a sudden and abrupt loss of detail when zooming out and a sudden and abrupt addition of detail when zooming in. For example, no local, secondary or connecting roads may be seen in FIG. 1 (at zoom level 5), although secondary and connecting roads suddenly appear in FIG. 2, which is the very next zoom level. Such abrupt discontinuities are very displeasing when utilizing the MapQuest website. It is noted, however, that even if the MapQuest software application were modified to permit a view of, for example, local streets at zoom level 5 (FIG. 1), the results would still be unsatisfactory. Although the visual density of the map would change with the zoom level such that at some level of zoom, the result might be pleasing (e.g., at level 7, FIG. 3), as one zoomed in the roads would not thicken, making the map look overly sparse. As one zoomed out, the roads would eventually run into each other, rapidly forming a solid nest in which individual roads would be indistinguishable.
The ability to provide smooth, continuous zooming on images of road maps is problematic because of the varying levels of coarseness associated with the road categories. In the United States, there are about five categories of roads (as categorized under the Tiger/Line Data distributed by the U.S. Census Bureau): A1, primary highways; A2, primary roads; A3, state highways, secondary roads, and connecting roads; A4, local streets, city streets and rural roads; and A5, dirt roads. These roads may be considered the elements of an overall object (i.e., a roadmap). The coarseness of the road elements manifests because there are considerably more A4 roads than A3 roads, there are considerably more A3 roads than A2 roads, and there are considerably more A2 roads than A1 roads. In addition, the physical dimensions of the roads (e.g., their widths), vary significantly. A1 roads may be about 16 meters wide, A2 roads may be about 12 meters wide, A3 roads may be about 8 meters wide, A4 roads may be about 5 meters wide, and A5 roads may be about 2.5 meters wide.
The MapQuest computer application deals with these varying levels of coarseness by displaying only the road categories deemed appropriate at a particular zoom level. For example, a nation-wide view might only show A1 roads, while a state-wide view might show A1 and A2 roads, and a county-wide view might show A1, A2 and A3 roads. Even if MapQuest were modified to allow continuous zooming of the roadmap, this approach would lead to the sudden appearance and disappearance of road categories during zooming, which is confusing and visually displeasing.
In view of the foregoing, there are needs in the art for new methods and apparatus for navigating images of complex objects, which permit smooth and continuous zooming of the image while also preserving visual distinctions between the elements of the objects based on their size or importance.